Process for removing inclusions present in a welding seam and device for executing said process

ABSTRACT

A process for removing inclusions ( 6 ), in particular silicates, present in the surface region of a welding seam ( 3 ), which is manufactured using shielding gas and which joins metallic components ( 4 ) to one another is designed in such a manner that the welding seam ( 3 ) is impinged by several jets ( 5 ) of a fluid medium that is subject to high pressure and by using different angles of incidence.

The present process relates to a process for removing inclusions presentin a welding seam in accordance with the preamble of the main claim 1 aswell as a device for executing said process.

While welding by means of shielding gas-welding procedures there areprecipitations of the components in the metal that are joined to oneanother by welding and/or the constituents of e.g. silicon, that arepresent in the welding filler materials that get deposited predominantlyas manganese silicate in the surface region of the welding seam.

Gas shielded arc welding can be carried out using various processes.Examples of such processes include metal-inert gas (MIG)-welding ormetal-active gas-welding using mixed gas (MAGM). Such deposits that arein a size range of 0.2 to 1 mm and are thus very small are distributedin an irregular pattern over the length and width of the welding seam.The silicates adhere very strongly to the weld metal. The overlapping ofthe seam material over the inclusion further intensifies this adherence.

Silicate-inclusions in the region of such undercuts cannot be removedusing the processes that are known from patent applications such as forinstance, JP 103 39 290 A (abstract) and DE 36 26 300 A1.

The latter document proposes the removal of inclusions by means of anabrasive high-pressure water jet using a fine-grained, sandy material asthe abrasive material.

However the application of such an abrasive material results in soilingthe components that have to be cleaned in a subsequent cleaning processin order to prepare them for further machining. This naturally involvesa considerable expenditure of labor and hence does not permit aneconomically efficient use of the said process. Therefore this processis not suitable for the machining of mass production components.

Even the abrasive effect of the blasting agent on the process devicessuch as robots etc. whose operability, at least with respect to theirdurability, can be severely restricted by the penetrating abrasivematerial proves to be very disadvantageous.

The said inclusions lead to an increased risk of corrosion thatadversely affects the strength of the welding seam in the course oftime. Most importantly, this factor works against the several effortsmade, for instance in the field of automotive engineering, for towardensuring a longer service life of welded components.

These non-metallic inclusions, in particular the silicates, have lesseradhesive forces than the material the forms the rest of the weldingseam. The lacking adhesiveness of the inclusions cause coating defectsif the component that is welded together is provided with a coating, forinstance, galvanization or a color application.

Such coating defects, besides affecting the visual overall impression ofthe device, also form potential corrosion spots.

The only option known so far to eliminate inclusions present in thesurface region of the welding seam reliably basically comprises of amachining operation, such as grinding etc. that produces metal particlesor shavings and in which even the regions that are free of inclusions,are inevitably processed at least in part.

However, a machining operation of such type involves very highexpenditure and thus works against the cost-effective manufacturing ofcomponents that are used as mass production components, for instance inthe field of automotive engineering.

Therefore, the task and objective underlying the present invention is tofurther develop a process of this kind so as to enable a reliable,economically efficient removal of inclusions in the welding seam.

This objective is achieved by a process having the characteristicsspecified in the main claim 1, as well as by a device pursuant to claim12.

As has been seen surprisingly, a thus executed machining operation ofthe welding seam removes the inclusions, in particular silicates,present in the surface region of the welding seam, where at least onejet of the fluid medium, preferably water, engages at the inclusions inthe border region of the adjoining material and detaches the existingjoint.

In doing so, the fluid medium is subject to a pressure of 1,500 to 4,000bar, preferably 2,500 to 3,000 bar.

Since the blasting of the individual inclusions cannot be carried out ina fixed direction or in a targeted manner, the entire surface of thewelding seam must be blasted. This can be carried out economically usinga rotating nozzle head comprising of several nozzles (n>=2). Inaccordance with the present invention, the individual jets of fluidmedium emerging from the nozzles impinge the welding seam at differentangles. This ensures that at least one jet reaches the weakestconnection point of the silicate on the metal and thus removes theinclusion.

The nozzles of the nozzle head are preferably adjusted to one another soas to facilitate the focusing by adjusting the gaps between them. Thisadjustment of the gaps between the nozzles can also be altered duringthe process pursuant to the present invention.

In a preferred embodiment of the invention, the nozzles are arrangedeccentrically in relation to the centerline of the nozzle head and atdifferent distances to the center of the rotation axis. In case of asmaller eccentricity an additional axially arranged nozzle can also beprovided.

Contrary to the prior art, the removal of the inclusions using a fluidmedium does not involve a machining operation that produces metalparticles or shavings if one disregards the detachment of the inclusionsand a possible abrasive effect on the welding seam on the whole so thatthe result is an extraordinarily effective machining process.Furthermore, this machining operation can be automatized completely,thus resulting in considerable cost advantages, while simultaneouslyoptimizing the surface of the welding seam with respect to corrosionresistance and/or coating ability. The latter allows for a completelyclosed coating that absolutely fulfils the desired purpose of corrosionprotection or surface design.

The machining of the welding seam in relation to both the machiningresult as well as the production-relevant data, for instance consumptionof energy or medium and speed of operation can be optimized using afluid medium, preferably water, that is subject to a pressure of 1,500to 3,500 bar, several outlet openings of the nozzle, each having adiameter of 0.4 to 0.8 mm, a feed speed of 60 to 90 mm/s, a nozzle speedof 1,000 to 2,000 min⁻¹ where the nozzle is at a distance ofapproximately 15 to 30 mm from the welding seam.

Additional advantageous embodiments of the present invention have beenspecified in the characteristics of the dependent claims. Exemplaryembodiments of the device in accordance with the present invention areset forth in the following description on the basis of the encloseddrawings of which:

FIG. 1 illustrates the side view of a device in accordance with thepresent invention in its operating position,

FIG. 2 illustrates an enlarged view of a detail illustrated in FIG. 1,

FIG. 3 illustrates a schematic bottom view of the device.

FIG. 1 illustrates a device for removing inclusions, in particular,silicates present in the surface region of a welding seam 3, which ismanufactured using shielding gas and with which two metallic components4 are joined to one another.

The device has a nozzle head 1 that is connected in a rotating and/oroscillating manner to a rotary drive that is not illustrated here.

In the present embodiment, the nozzle head 1 is provided on its end sidewith three nozzles 2, from each of which a jet 5 of fluid medium emergesthat is subject to high pressure such that the angles of emergence a1 toa3 are adjusted variably inwards, that is to one another and impinge thewelding seam 3 at corresponding angles of incidence.

As can be seen clearly especially in FIG. 3, the nozzles 2 are arrangedeccentrically to the rotation axis of the nozzle head 1 and at differentdistances e1 to e3 to one another.

Due to the different angles of incidence, the various eccentricities ofthe nozzles 2 as well as the rotating and/or oscillating movement of thenozzle head 1, each surface region of the welding seam 3 is impinged bya high pressure jet 5 where the nozzle head can be mounted in such amanner that its progression corresponds to that of the welding seam tobe processed, for instance, on a robot etc. when the correspondingworkpiece is placed in a stationary position. Alternately the workpiececan be moved in relation to the nozzle head 1, which is then stationary.Either of these cases reliably enables, with the help of any of the jets5, the detachment of the existing inclusions 6 from their joint with thewelding seam.

The complete device can be mounted in such a manner that its progressioncorresponds to that of the welding seam to be processed, for instance ona robot etc. when the corresponding workpiece is placed in a stationaryposition.

However, it is also feasible to move the workpiece in relation to thedevice, which is then stationary.

1. A process for removing inclusions in particular, silicates, presentin the surface region of a welding seam, which is manufactured usingshielding gas and which joins metallic components to one another,wherein the welding seam is impinged by several jets of a fluid mediumthat is subject to high pressure and by using different angles ofincidence
 2. The process pursuant to claim 1, wherein the jets areapplied at the same time.
 3. The process pursuant to claim 1, whereinthe jets are applied onto the welding seam in a rotating and/oroscillating manner
 4. The process pursuant to claim 1, wherein at leasta few of the individual jets are adjusted to one another and extend inan inclined manner
 5. The process pursuant to claim 1, wherein the jetsare guided continuously in the direction of the welding seam
 6. Theprocess pursuant to claim 1, wherein the welding seam is moved inrelation to the region of incidence of the jets
 7. The process pursuantto claim 1, wherein the jets are guided at variable distances (e1 to e3)from a nozzle head
 8. The process pursuant to claim 1, wherein at leastone jet is guided axially in relation to the centerline of the nozzlehead
 9. The process pursuant to claim 1, wherein the fluid medium issubject to a pressure of 1,500 to 4,000 bar.
 10. A device for executingthe process pursuant to claim 1, wherein an arrangement is provided thatcomprises of several nozzles for a fluid medium that is subject to highpressure and that the nozzles extend at variable angles of inclination(α1-α3).
 11. A device pursuant to claim 10, wherein at least a few ofthe nozzles are adjusted to one another and extend in an inclinedmanner.
 12. A device pursuant to claim 10, wherein the nozzles arearranged in a nozzle head.
 13. A device pursuant to claim 10, whereinthe nozzle head can be moved in a rotating and/or oscillating manner.14. A device pursuant to claim 10, wherein said device can be moved inrelation to the welding seam to be processed.
 15. A device pursuant toclaim 10, wherein the relative movement of the device or of theworkpiece provided with the welding seam amounts to approximately 60 to90 mm/s.
 16. A device pursuant to claim 10, wherein the speed of thenozzle head during operation is approximately 1,000 to 2,000 min⁻¹. 17.A device pursuant to claim 10, wherein the diameter of the nozzles isapproximately 0.4 to 0.8 mm.